Austin Water staff said the department is expanding consultant work to compare three near‑term water‑supply options: indirect potable reuse (IPR) discharging treated reclaimed water into Lady Bird Lake, using Lake Walter E. Long (often called Decker Lake) as a municipal supply reservoir, and direct potable reuse. The work will feed a feasibility report planned for early fall 2025.

“Indirect potable reuse was characterized as a drought emergency strategy that we would only implement when combined storage at the Highland Lakes reached 400,000 acre‑feet,” Marissa (Austin Water staff) told the task force, citing the Water Forward 2024 planning assumptions. She said the IPR footprint in the Water Forward plan targets about 22,400 acre‑feet per year of yield and that the project was preliminarily targeted for substantial completion in 2028, though costs and timing are still being refined.

Marissa summarized how the two main options under discussion would work operationally. For IPR through Lady Bird Lake, staff said the plan is to treat wastewater effluent from the South Austin Regional (SAR) wastewater treatment plant to reclaimed‑water quality, perform additional treatment under a TCEQ permit and discharge to Lady Bird Lake near Longhorn Dam. A new intake and pump station upstream at Tom Miller Dam would then withdraw treated lake water to Ulrich Water Treatment Plant for potable treatment and distribution.

For use of Lake Walter E. Long as a supply reservoir, staff described diverting Colorado River water at the existing diversion point downstream of Walnut Wastewater Treatment Plant and conveying or holding that water in Walter E. Long, then treating it at a new treatment plant sized to the anticipated yield. Staff noted that Decker/Walter E. Long already receives upstream wastewater effluent and historically has been used for industrial (power plant cooling) and recreation; the planned municipal use would require additional treatment and potentially water‑right amendments.

Costs and relative timing: staff said the Walter E. Long option carries higher capital cost — roughly two‑and‑a‑half times the per‑acre‑foot and total cost in planning‑level comparisons — but that IPR costs could rise if the preferred configuration requires more extensive upgrades at SAR rather than separate side‑stream treatment facilities. Marissa said recent discussions about SAR expansion prompted staff to reconsider whether side‑stream facilities or whole‑plant improvements would be more appropriate and whether that would increase cost and schedule for IPR.

Bill Moriarty (task force appointee) urged caution about abandoning IPR. “I wouldn’t give up on this too quickly… IPR is way better” for resilience than relying on another lake, he said, adding that the side‑stream treatment issue felt “very solvable.” Marissa responded that staff have not abandoned IPR but want to reevaluate priorities and run an apples‑to‑apples comparison of options before moving forward with permit submittals or contract actions.

Consultants and studies: staff said the city has retained Plummer to perform IPR planning and comparative analysis, Hazen & Sawyer to support intake/pump station conceptual planning, and CAS to develop routing options for reclaimed transmission mains from SAR to Lady Bird Lake. Staff also said they are preparing an interlocal agreement with the Texas Water Development Board for sediment and bathymetric surveys of Lake Austin and Lady Bird Lake and hoped to have that agreement executed in summer 2025.

Permits and regulatory considerations: staff said IPR to Lady Bird Lake would require a TPDES (TCEQ) permit to authorize discharge; the permitting outcome will define treatment targets and thus influence technology and cost. For Walter E. Long, staff said the city would pursue municipal‑use amendments to existing water rights; preliminary conversations indicate an amendment could make about 16,000 acre‑feet available under an administrative approach, with longer‑term water‑right changes possible for additional volume.

Planned next steps: Plummer’s expanded scope will evaluate IPR configurations (side‑stream treatment vs. whole‑plant improvements), Walter E. Long as a reservoir and a direct potable reuse option. Staff expect the consultant evaluation to be complete in June–July and to deliver a feasibility memo in early fall 2025. Meanwhile, the city will continue planning for reclaimed transmission mains and an intake/pump station on Lady Bird Lake that would be useful under multiple options.

Ending: Task force members asked staff to include water‑quality sampling plans for Walter E. Long (the city has requested an 12‑month sampling program) and to clarify how LCRA demand assumptions are used in storage projections. Staff said they will continue monthly coordination with Watershed Protection, Austin Energy and PARD on Lake Walter E. Long issues and will return to the task force with the consultant’s comparative evaluation.